1. Technical Field
The present invention relates to semiconductor processing and more particularly to a device and methods for forming lithographic and sub-lithographic features on or in a semiconductor device.
2. Description of the Related Art
Lithography is employed in many applications to pattern layers in semiconductor processing. One process where lithography is useful includes the process for producing contact holes. As dimensions shrink in semiconductor devices, forming contact holes becomes increasingly difficult. With current technology, reliably defining contact holes with reproducible size is a major hurdle for semiconductor manufacturing. Building very-reproducible sub-lithographically-dimensioned “holes” or trenches/troughs is needed.
Methods for producing small-dimension contact holes typically involve the use of optical lithography to print “larger” holes. These larger holes can then be shrunk to necessary (sub-lithographic) dimensions by depositing (and etching) spacers on the hole sidewalls. This process, however, produces holes with dimensional tolerances of at least the same magnitude as the original photo tolerance. For example, if a 100 nm hole is printed with ±10% tolerance, and the spacer process adds ZERO additional tolerance (which is virtually impossible), then adding 25 nm spacers will result in a hole of dimension 50 nm ±20%.
This increased percentage variability is often intolerable, and decreased tolerances are required.
Sidewall Image Transfer (“SIT”) has been employed as a method for building sub-lithographic features. SIT offers opportunities to produce features with tolerance improved over that of the defining lithography. However, SIT is ideally suited for producing lines, not spaces or holes, and converting lines to holes is costly. Even if, SIT troughs are made, making discrete round or square holes is not currently possible employing SIT, which naturally makes only continuous-loop shapes. Further, even if SIT could be employed, SIT would need an additional mask to cut resulting loop shapes into discrete features.